One Do Not Track (DNT) expert, however, didn't think Yahoo's decision, announced last week, would affect its deal with Microsoft.

"I don't think this is especially significant," said Justin Brookman, director of consumer privacy at the Center for Democracy and Technology. "Yahoo! is just the biggest individual company to draw this line in the sand. I doubt this will affect their search relationship." Brookman has been heavily involved in the DNT standard-setting effort.

Dan Olds, an analyst with the Gabriel Consulting Group, agreed. "This won't rise to the level where it will affect the Yahoo-Microsoft relationship. Companies this large are able to compartmentalize."

IE10, which launched Oct. 26 alongside Windows 8 and will be released as a preview for Windows 7 by mid-November, is the only browser that has switched on Do Not Track (DNT) by default.

In reality, some argue, IE10 does not actually switch DNT on: In August, , and promised that during Windows 8 setup, customers will be notified of the impending setting and given a chance to turn it off.